Xamarin中如何获取上一个Page/Activity？

Hey there! Great question—tracking the previous page or activity isn't something that's built right into the framework by default, but there are a few solid, platform-specific ways to make this work. Let's break it down based on what you're working with:

If you're dealing with Android Activities, here are two reliable approaches:

• Pass the previous activity name via Intent
  This is the simplest and most straightforward method for most cases. When you launch a new Activity from the current one, just add the current activity's name as an extra to the Intent:

  // In your current Activity (e.g., MainActivity)
  Intent intent = new Intent(this, NextActivity.class);
  intent.putExtra("previousActivityName", this.getClass().getSimpleName());
  startActivity(intent);
  

  Then in the target Activity, retrieve the value:

  // In NextActivity
  String previousActivity = getIntent().getStringExtra("previousActivityName");
  

  No special permissions needed, and it works across all Android versions.

• Manual navigation stack (for more complex flows)
  If you need to track navigation history across multiple screens, create a singleton class to maintain a stack of activity names:

  public class NavigationHistory {
      private static NavigationHistory instance;
      private Stack<String> activityStack = new Stack<>();
  
      private NavigationHistory() {}
  
      public static NavigationHistory getInstance() {
          if (instance == null) {
              instance = new NavigationHistory();
          }
          return instance;
      }
  
      public void pushActivity(String activityName) {
          if (!activityStack.contains(activityName)) {
              activityStack.push(activityName);
          }
      }
  
      public String getPreviousActivity() {
          if (activityStack.size() >= 2) {
              // Pop current to access the one before it, then push back
              String current = activityStack.pop();
              String previous = activityStack.peek();
              activityStack.push(current);
              return previous;
          }
          return null; // No previous activity exists
      }
  }
  

  Call NavigationHistory.getInstance().pushActivity(this.getClass().getSimpleName()) in each Activity's onResume() method, then use getPreviousActivity() whenever you need the prior screen's name.

Note: Avoid using ActivityManager to fetch the task stack on Android 11+—the GET_TASKS permission is restricted now, so it won't work reliably for most apps.

For .NET-based UI frameworks using Pages, these methods will do the trick:

• Leverage the built-in Navigation Stack
  If you're using a NavigationPage for navigation, the framework already maintains a stack of Pages you can access directly:

  if (Navigation.NavigationStack.Count >= 2)
  {
      var previousPage = Navigation.NavigationStack[Navigation.NavigationStack.Count - 2];
      string previousPageName = previousPage.GetType().Name;
  }
  

  Just make sure to check the stack count first to avoid index out-of-range errors (this handles cases where the current page is the first one in the stack).

• Custom navigation history stack
  If you're not using NavigationPage or need more control over history tracking, create a static class to manage the stack:

  public static class PageNavigationHistory
  {
      private static readonly Stack<string> _pageStack = new Stack<string>();
  
      public static void TrackPage(string pageName)
      {
          // Avoid adding duplicates if the page is reloaded
          if (_pageStack.Count == 0 || _pageStack.Peek() != pageName)
          {
              _pageStack.Push(pageName);
          }
      }
  
      public static string GetPreviousPageName()
      {
          if (_pageStack.Count >= 2)
          {
              string currentPage = _pageStack.Pop();
              string previousPage = _pageStack.Peek();
              _pageStack.Push(currentPage);
              return previousPage;
          }
          return null;
      }
  }
  

  Call PageNavigationHistory.TrackPage(this.GetType().Name) in each Page's OnAppearing() method, then use GetPreviousPageName() to fetch the prior page's name when needed.

内容的提问来源于stack exchange，提问作者Ian Gallegos